Sigma Gamma Rho Sisterhood T Shirt Mathematical symbol icon sigma, vector illustration Stock Vector Sigma summation symbol. Math sigma sign vector. Mathematics resources What Does the Term Sigma Male Mean? 7ESL Sigma summation symbol. Math sigma sign vector. Mathematics resources. A must have for members of Sigma Gamma Rho sorority, this Sisterhood t shirt is made of high quality cotton and features the iconic SGR logo. Perfect for wearing around campus or at events, this t shirt is sure to show your sorority pride.